Devices in computer systems can perform varying functions. For example, devices such as microprocessors can execute instructions while devices such as disk drives can store instructions and data. In order for such devices to communicate, they each need to conform to an interface protocol. Interface protocols typically specify a means for multiple devices to communicate. The means for communicating, however, can vary widely between different interface protocols.
A traditional interface protocol that is used by devices such as hard disk drives and CD-ROM drives is often referred to as the IDE (“Intelligent Disk Electronics”), ATA (“Advanced Technology Attachment”), or IDE/ATA interface protocol. The IDE/ATA interface protocol is defined by a set of standards adopted by the American National Standards Institute, Inc. These standards include “Information Systems—AT Attachment Interface for Disk Drives” (ANSI X3.221-1994), “Information Technology—AT Attachment Interface with Extensions (ATA-2)” (ANSI X3.279-1996), “Information Technology—AT Attachment-3 Interface (ATA-3)” (ANSI X3.298-1997), and “AT Attachment with Packet Interface Extension (ATA/ATAPI-4)” (ANSI NCITS 317-1998). There are numerous variations of the IDE/ATA interface protocol, such as ATA/ATAPI, EIDE, ATA-2, and Ultra ATA. The current standards that define the various IDE/ATA interface protocols will be collectively referred to herein as the IDE/ATA protocol or IDE/ATA interface, and hard disk drives configured to operate using the IDE/ATA interface will be referred to as IDE/ATA drives. The standards may be obtained from ANSI, 11 West 42nd St., New York, N.Y. 10036 or http://www.ansi.org.
Another interface protocol often used with storage subsystems is the Small Computer System Interface (“SCSI”). As with the IDE/ATA interface, there are numerous variations of the SCSI interface, such as SCSI-1, Wide SCSI, Fast SCSI, Ultra SCSI, etc. As used herein, the terms “SCSI interface” or “SCSI interface protocol” are intended to refer to any of the variations of the SCSI interface. The SCSI interface has been used, for example, by host computers for I/O communications with storage subsystems. These host computers communicate with the storage subsystem using SCSI commands, and the storage subsystems transmit these SCSI commands to SCSI-compliant hard disk drives.
Fibre Channel (“FC”) is an industry-standard, high-speed serial data transfer interface that can be used to connect systems and storage in point-to-point or switched topologies. Many varying types of devices can be connected using the FC protocol over large distances. These devices include servers, workstations, storage devices, hubs, and switches. The FC protocol is defined by a set of standards adopted by the American National Standards Institute, Inc. (ANSI). These standards include “Information Technology—Fibre Channel—Physical and Signaling Interface (FC-PH)” (ANSI X3.230-1994), “Information Technology—Fibre Channel Physical and Signaling Interface (FC-PH)—Amendment 1” (ANSI X3.230-1994/AM 1-1996), “Information Technology—Fibre Channel—Physical and Signalling Interface-2 (FC-PH-2)” (ANSI X3.297-1997), and “Fibre Channel Physical and Signalling Interface-3 (FC-PH-3)” (ANSI X3.303-1998). The standards that define the FC protocol will be referred to collectively as the Fibre Channel or FC protocol. The standards may be obtained from ANSI, 11 West 42nd St., New York, N.Y. 10036 or http://www.ansi.org. The FC standard defines a layered protocol architecture consisting of five layers, the highest defining mappings from other communication protocols onto the FC fabric. FC can serve as the physical transport for other command protocols, including the SCSI command protocol and Internet Protocol (“IP”).
While interfaces such as those defined by the IDE/ATA protocol, the FC protocol, and the SCSI protocol are used widely, these protocols do not provide a means for interfacing with the other. In general, IDE/ATA compliant devices are less expensive than FC and SCSI compliant devices; however, IDE/ATA compliant devices have typically not been suitable for high-end computer systems because of protocol and distance limitations. Thus, the more expensive FC compliant devices have typically been employed within high-end computer systems.